Without limiting the scope of the invention, its background is described in connection with current methods of forming electrical connections to high dielectric constant materials, as an example.
High dielectric constant (hereafter abbreviated HDC) materials exhibit high dielectric constants (generally greater than 20) which make them useful for the fabrication of many electrical devices, such as capacitors. Examples of these HDC materials include titanates such as barium strontium titanate and lead zirconium titanate, titanates doped with one or more acceptors such as alkaline earth metals (i.e. group IIA elements), and titanates doped with one or more donors such as rare earth elements (i.e. the lanthanide series elements plus yttrium). Many ferroelectrics and transition metal oxides (i.e. oxides of elements with atomic number 21-29, 39-47, 57-79, and 89 and above) also exhibit high dielectric constants. To be useful in electronic devices, however, reliable electrical connections must be constructed which do not diminish the beneficial properties of these HDC materials.
Heretofore, in this field, single and multiple metal layers are generally used to form electrical contacts to HDC materials. For example, to provide an electrical connection to an HDC material which makes up a capacitor on the surface of a semiconductor substrate, the following techniques are among those now employed: (a) dielectric/platinum/substrate, (b) dielectric/platinum/tantalum/substrate, (c) dielectric/gold/substrate, (d) dielectric/gold palladium/substrate, (e) dielectric/gold palladium/tungsten/substrate. The layering sequence in these examples is from the top down to the substrate (e.g. silicon). A similar metallization scheme is required for the top of the dielectric film to complete the capacitor structure. In general, current approaches use a noble metal to contact the dielectric in conjunction with another metal to serve as a sticking layer.